Conventionally, endoscopes have been widely used in the medical field and the like. With an endoscope, for example, internal organs in a body cavity can be observed by inserting an elongated insertion portion into the body cavity, and various treatments can be performed using a treatment instrument inserted into a treatment instrument insertion channel as necessary. At a distal end of the insertion portion, a bending portion is provided. By operating an operation portion of the endoscope, observing direction of an observation window at a distal end portion can be changed.
In general, an endoscope is provided with an air/water feeding nozzle for cleaning for a case where body fluid or the like adheres on an outer surface of the objective optical system of the endoscope to disturb the observation when the endoscope is inserted into the body cavity. The outer surface of the objective optical system of the endoscope can be secured of a clean observation field of view with, for example, a cleaning liquid spouted out or air sprayed from the air/water feeding nozzle.
For example, an endoscope having a plurality of objective optical systems is proposed as described in Japanese unexamined patent publication No. 06-154155. This endoscope has a plurality of image pickup units, wherein the plurality of objective optical systems and an aperture of an air/water feeding nozzle are located at a distal end of an insertion portion to line up on a generally straight line. In order to obtain images by the image pickup units, the endoscope has two illumination optical systems for irradiating illumination light into the body cavity where almost no natural light enters.
Further, in recent years, there have been endoscopes that can perform, in addition to normal light observation for picking up an image in the body cavity which is generally the same as in naked-eye observation by irradiating mainly white light or RGB light by the frame sequential method into the body cavity, special light observation such as, for example, fluorescent light observation, that can specify a lesion region existing in a diseased part which is difficult to be diagnosed by the normal light observation, by irradiating light having a specific wavelength band into the body cavity to pick up an image of the diseased part.
However, in an endoscope described in Japanese unexamined patent publication No. 06-154155, there is a problem that a region to be inspected cannot be iiradiated with enough amount of illumination light, due to absence of consideration for cleanability by liquid or gas from an air/water feeding nozzle for cleaning outer surfaces of two illumination optical systems when the outer surfaces of the two illumination optical systems are adhered with mucous membrane, blood, filth or the like in the body cavity. The endoscope has another problem that, in a large intestine, for example, which is a body cavity, the two illumination optical systems are covered by folds of the intestine, thereby blocking the illumination light from reaching the region to be inspected.
Moreover, in the case of, for example, fluorescent light observation as a special light observation to be performed in the body cavity, since a lesion region in a diseased part emits only a small amount of fluorescent light, second illumination means used for the special light observation is required to receive the fluorescent light emitted from the lesion region in as large an amount as possible. Therefore, it is possible that an object optical system used in fluorescent light observation is rendered incapable of showing enough observation performance of, for example, a fluorescent light image pickup unit for special light observation, when an outer surface of the object optical system is adhered with mucous membrane, blood, filth or the like present in an optical axis direction thereof, or when the observation field of view is obstructed by folds of a body cavity, particularly, an intestine.
Incidentally, among special light observations to be performed in a body cavity, in the case of, for example, the fluorescent light observation, when there is a lesion region in a diseased part, which emits only a small amount of fluorescent light, it is necessary to receive the fluorescent light emitted from the lesion region in as large an amount as possible. Therefore, in fluorescent light observation, it is necessary to irradiate the lesion region with larger amount of illumination light than in normal light observation.
Thus, in an endoscope having a plurality of image pickup units, it is necessary that light having a specific wavelength band that is irradiated into a body cavity from the illumination optical system in fluorescent light observation is more surely irradiated to the lesion region of the diseased part than white light or RGB light by the frame sequential method that is irradiated into the body cavity from an illumination optical system in normal light observation.
However, in the endoscope of the Japanese unexamined patent publication No. 06-154155, no specific description is made about disposition of the illumination optical system used for special light observation such as fluorescent light observation, and there have been problems as mentioned above.
Thus, in view of the above-described circumstances, an object of the present invention is to provide an endoscope insertion portion of an endoscope capable of showing enough of good observation performance by distributing a plurality of image pickup means with necessary amount of illumination light, in particular, ensuring good amount of observation light to be incident on an image pickup unit for special light, which is required to be received in as large an amount as possible, as well as showing enough observation performance of an image pickup unit for special light.